Fluid cooled hollow cathode discharge tube



G. CIRRI sept. 1o, 196s FIUID COOLED HOLLOW CATHODE DISCHARGE TUBE FiledJune 17, 1966 0 2 d 5 M W INVETOR United States Patent O 3,401,292 FLUIDCOOLED HOLLOW CATHODE DISCHARGE TUBE Gianfranco Cirri, Florence, Italy,assigner to Fabbrica Italiana Valvole Radio Elettriche F.I.V.R.E.S.p.A., a

corporation of Italy Filed June 17, 1966, Ser. No. 558,381 7 Claims.(Cl. 313-32) ABSTRACT OF THE DISCLOSURE A cooling means for a hollowcathode tube used in spectrophotometry characterized in that the cathodeholder is surrounded by a coaxial body which is spaced therefrom forminga cooling circuit substantially over the entire length of the cathode.An annular baille is mounted between the cathode holder and the coaxialbody to form two separate pathways for the cooling fluid, the pathwaysVbeing respectively connected to a cooling lluid inlet and outlet.

This invention relates to a hollow cathode turbe for `application inspectrophotometry.

Tubes of this type, as it is known, may be applied, for example, as wavelength reference generators and to determine in conjunction with a'burner and photoelectric cell, the contents of certain substances in agiven sample material, as, for example, metals.

In applications of the latter type, a light beam emitted by the cathodeand directed upon a photocell is absorbed by the llame to a variabledegree due to the combustion of the substance to be determined, if thisis the same as that of the cathode.

The content of the substance contained in the cathode may be determinedby the light variations on the photoelectric cell.

The operating temperature of the tube must be as constant as possible soas to maintain the light emitted by the cathode constant, so that thelight variations registered =by the photoelectric cell are those due tothe presence of a substance in the flame similar to that contained inthe cathode of the tube.

lFrom this point of view, it can then be understood, also with referenceto other applications, how hollow cathode tubes used inspectrophotometry must be adequately cooled in order to st-abilize theoperating temperature.

One object of this invention is precisely that of providing a hollowcathode tube with temperature stabilization means and adapted to insureconstant and steady emission of light as well as a rapid achievement ofa steady operating condition and cathode sputtering control.

A further object of the invention is that of providing a tube of thehighest elliciency long life and linear response.

In this invention, the above objectives are achieved by ellicientcathode cooling and for this purpose the cathode support or holder issurrounded by a hollow element coaxial to it and the inner part of whichis provided with means which help to define the fluid cooling circuitfor the cathode.

Said cooling circuit substantially extends over the entire length of thecathode.

According to this invention, one of the ends of the hollow body has atube extension which receives a tube for circulation of the fluid andwhich terminates at the top of the cathode with a bafile which dividesthe interior of the hollow body into intercommunicating chambers inwhich the cooling iluid circulates.

Another characteristic of the invention is that the an- Cir PatentedSept. 10, 1968 ode of the tube conveniently consists of an envelopewhich surrounds the cathode holder or support, and which extends beyondthe cathode to be supported at one end by the bulb of the tube withwhich it is engaged by a suitable collar which also serves as a terminalclamp for polarity.

According to a further aspect of the invention, a metal tube element isprovided between the cathode and the glass bottom or optical window ofthe tube and which tube element acts both as a second anode and aprotection for the optical window.

The invention will now be described in detail in conjunction with theattached drawing, by way of example, and in which the illustration showsthe cathode tube according to the invention.

The tube illustrated consists of a glass bulb filled with a rare gas,and having two complementary sections A1 and A2 communicating with eachother and sealed air tight, as will be described hereinafter.

The end of section A1 is closed by a metal ybottom piece 10, the rim ofwhich is connected, in air tight relation7 for example, by welding, tothe rim of said section A1.

A tube shaped spigot 12 is secured air tight, for example, by welding,to said bottom piece and extends to the exterior of section A1 for acertain length. Spigot 12, in the case illustrated, for-ms an integralpart of a hollow body 14, the interior of which communicates with thebore of said spigot or tube extension.

Body 14 is closed, air tight, at its other end, by flange 16 of acathode support 18 extending into s'aid hollow -body and which isprovided with suitable means, for example, threads, for securing cathode20 of the tube which, as stated, is hollow.

The end of spigot 112, extending from section A1 is provided with agroove 24 which serves to secure a threaded vbushing 22 to the spigotitself and which is provided with an eye-bolt 24 to engage said groove.Groove 24' also serves as an electrical connecting means between thelelectric power source and cathode of the tube.

A manifold 26 is secured in air tight relationship to the end of 4spigot12 by means of a bushing 22 which is screwed to it. The manifold has aninner chamber 28 which is connected to a pipe connection 30 for thecooling lluid outlet. Manifold 26, in turn, is crossed by a tu'bel 34which, passing through the inner part of spigot 12, communicates withthe interior of hollow body 14.

Chamber 28 communicates with the inside of hollow body 14 through a portlocated between tube 34 and spigot 14.

The inner end 36 of tube 34 extends into -a bored space element 38 whichis secured to the hollow body 14 which has an annular baille 40, `whichdivides the interior of hollow body 14 into two separate chambers.

It should be noted that manifold 26 which carries tubes 30 and 34 andbushing 22 forms a lixed separate unit which is mounted on the hollowcathode tube by introducing tube 34 into the central bore of spacerelement 38 and by subsequently securing the bushing to the end of spigot12 by eye-bolt 24 as previously stated.

Cooling of cathode 20 is obtained by means of the lluid which, afterentering tube 34 and discharging at its end 36, strikes the bottom 15 ofcathode support 18 and successively, after being guided in its path bythe inner surface of baille 40, strikes the external side Iwall ofcathode support 18 to reach the bottom end flange 16 of the latter,after which the fluid reverses its llow direction passing into thechamber formed by baille 40 and hollow body 14, the ports in spacerelement 38, the space between tube 34 and spigot 12 and finally todischar-ge from chamber 28 into pipe 30.

latter entirely surrounds the cathode itself and its entire surface isconstantly in contact with the owing fluid.

The cathode cooling circuit above described ensures uniform and regularcirculation of the cooling uid and thus a stability of temperature inthe cathode which thus guarantees a constant emissivity of light.

Insofar as the rapid achievement of a stable operating condition isconcerned, it should be noted that this is almost immediately achieved,by virtue of the eicient cathode cooling.

The hollow cathode tubes heretofore known required an average ofapproximately 20-30 minutes before reaching a stable operating conditionand, moreover, were not suitable to provide a light emissivitysufficiently constant to consent the relative measurement in addition toabsolute measurement, which it is possible on the other hand to obtainwith the tube forming the object of this invention, by virtue of itsconstant emission of light over a given time.

In order to provide high efficiency and long life, the anode of the tubeconsists of an envelope or shield 50 having a cylindrical part 51 whichsurrounds most of hollow body 14 and a conical connecting surface 52which extends beyond the cathode and is locked by a flan-ge 54 weldedair tight between the edges of the two bulb sections A1 and A2.

The arrangement of the anode around the cathode results in a highereiciency of the working discharge (taking place in the cathode cavity)because the parasite discharges (such as occur outside the cathode holein the known tubes) are practically eliminated by virtue of the anodecoaxial structure which is suitably sized according to the cathodedimension.

Moreover, this arrangement makes its possible to extend the tubes lifeto hitherto unknown limits as a result of the very great reduction inabsorption of the rare gas contained in the tube itself, both becausethe ionized gases cannot come into contact with the glass parts of thetube and because of the suppression of parasite clischarges as well ascontrol of sputtering emitted by the cathode (at constant temperature).

The edge of flange 54 conveniently extends to the exterior of the tubefor connection with the anodic supply.

The bulb is then closed air tight at the end of section A2 by atransparent lglass bottom plate 60 representing the optical window andconnected to the bulb by metal parts consisting of a ring 58 and liange56.

Although the spectrophotometric tube as illustrated and f described hasprovided excellent results, it was noted that this could be furtherimproved by the introduction of suitable changes.

We have noted in fact that under some operatin-g conditions or withcertain filling gases or cathode materials, the optical window of thetube may not be sufficiently protected from the cathode sputtering, andthat its transparency may consequently be reduced.

To insure the best efiiciency of the tube, under any and all operatingconditions, with any type of lling gas or cathode material, a hollowmetallic element or tube 61 is placed between the cathode and theoptical windo-w 60, said metal element 61 having a cone shaped flange 62by which it is secured to metal ring 58. The other end of the tube isfree and extends to the neighborhood of the cathode.

The above hollow element 61, the length and internal diameter of whichare suitably proportioned to the dimensions of cathode 20 and functionof the tilling gas, provides a protection of window 60 from the cathodesputtering and also contributes, if suitably polarized with respect tothe cathode and coaxial anode 50-52, to avoid the formation of parasitedischarges, with consequent improvement of the efficiency of the workdischarge and life of the tube.

In the latter function it acts as a second anode for the tube,polarization being insured by ring 58 of the bottom plate.

I claim:

1. A hollow cathode tube for spectrophotometry provided with cathodecooling comprising glass bulb means, hollow cathode means, means tosuppont said cathode in said bulb including a hollow body and a tubularportion integral with one end of said body and extending out of saidglass bulb, an annular chamber formed by said hollow body beingco'axially ymounted spaced from said cathode and extending oversubstantially the entire length thereof, means for mounting said cathodein the free end of said hollow body, annular baffle means coaxiallymounted in said chamber forming inner and outer separate uid pathways,cooling uid inlet means passing through said tubular :portion andintegral with said baflie to feed only said inner pathway, cooling fluidexhaust means connected to said tubular portion no receive cooling fluidfrom said outer pathway, means for supplying power to said cathode,anode means comprising an envelope coaxially mounted about said hollowbody, said envelope comprising a cylindrical portion and an integralconical portion the flared end of which extends beyond said cathode sothat coolant discharge will not affect the glass bulb, said conicalportion extending through said glass bulb thus forming electricalconnection imeans for said anode.

2. A hollow cathode tube according to claim 1 further comprisingmanifold means, said manifold means being mounted in air-tightrelationship on said tubular )portion 0f said cathode support, ringmeans and locking terminal means sealing said manifold on said tubularportion, electrical connection means for said cathode formed by saidring means, locking tenminal means and cathode supporting means.

3. A Vhollow cathode tube according to claim 1 further comprising anvoptical window formed in said glass bulb, a hollow metal element xedlymounted axially between said cathode and said optical window.

4. A hollow cathode tube according to claim 3 further comprising -ametal ring secured to the periphery of said optical Window, one end ofsaid hollow metal element being secured to said ring and the other endof said hollow metal element terminating in the neighborhood of saidhollow cathode.

5. A hollow cathode tube according to claim 3 in which said hollowmetall element is a tube.

6. A hollow cathode -tube according to claim 4 in which said hollowmetal element has a conical flange on one end thereof, said ange beingsecured to said ring.

7. A hollow cathode tube according to claim 3 in which said hollow metalelement forms a second anode which is suitably polarized with respect tosaid cathode and first anode.

References Cited UNITED STATES PATENTS 2,647,218 7/1953 Sorg et al313-247 2,802,125 8/1957 Nedderman 313-32 2,807,746 9/1957 Gardner et al313-32 X 3,305,742 2/1967 McCune 313-36 X l AMES W. LAWRENCE, PrimaryExaminer.

D. J. GALVIN, Assistant Examiner.

